What Is a Portlet

Sky-Tiger

Every portlet application is a web application, so it requires a web.xml file in addition to portlet.xml. <web-app>
  <display-name>Hello World Portlet
  </display-name>
  <welcome-file-list
    <welcome-file>index.jsp
        </welcome-file>
  </welcome-file-list>
</web-app>
The next step is compiling this content and packaging it into a .war file. You can do that yourself or download the sample code (see the "Resources" section) that has a build.xml that your can use for creating the .war file.

Sky-Tiger

Deploying HelloWorld Portlet on Pluto
Pluto is in the early stages of development, so it does not have a set of easy-to-use administrative tools. In order to use the Pluto server, you will have to download both the binary and source versions. Please note that these instructions are for Windows; Unix users can get similar results by changing slashes and using .sh shell scripts rather than .bat batch files.

Create a folder, such as C:\PlutoInstallation.
Download pluto-1.0.1-rc1.zip and pluto-src-1.0.1-rc1.zip from the Pluto website.
Extract pluto-1.0.1-rc1.zip into C:\PlutoInstallation. It should get extracted in C:\PlutoInstallation\pluto-1.0.1-rc1.
Start Pluto by calling C:\PlutoInstallation\pluto-1.0.1-rc1\bin\startup.bat.
You are ready to access your Pluto server at http://localhost:8080/pluto/portal.

Extract pluto-src-1.0.1-rc1.zip to C:\PlutoInstallation\PlutoSrc.
Go to C:\PlutoInstallation\PlutoSrc and run maven distribute:all.. This should build and download necessary dependencies required for running common admin tasks.
Now it is time to install our HelloWorldPortlet.war as a portlet.

Sky-Tiger

First, copy HelloWorldPortlet.war to the C:\PlutoInstallation\portlets directory, creating the directory if necessary.
Rename C:\PlutoInstallation\plutosrc\build.properties.sample to build.properties.
Open build.properties and change it so that maven.tomcat.home points to the Pluto binary installation. In our example, this will be maven.tomcat.home=C:/PlutoInstallation/pluto-1.0.1-rc1.
To install your portlet, go to C:\plutoInstallation\plutosrc\deploy and run maven deploy -Ddeploy=c:\PlutoInstallation\portlets\HelloWorldPortlet.war. You should get a "build successful" message.
In C:\PlutoInstallation\pluto-1.0.1-rc1\webapps, you should see a folder for HelloWorldPortlet.
Now, open the web.xml file of your installed portlet by going to the C:\PlutoInstallation\pluto-1.0.1-rc1\webapps\HelloWorld\WEB-INF\ folder. You will see that a few lines are automatically added to this file, like this: <servlet>
  <servlet-name>HelloWorld</servlet-name>
     <display-name>HelloWorld Wrapper</display-name>
      <description>Automated generated
      Portlet Wrapper</description>
      <servlet-class>org.apache.pluto.core.PortletServlet
      </servlet-class>
      <init-param>
         <param-name>portlet-class</param-name>
         <param-value>com.test.HelloWorld
         </param-value>
      </init-param>
      <init-param>
         <param-name>portlet-guid</param-name>
         <param-value>HelloPluto.HelloWorld
         </param-value>
      </init-param>
</servlet>

Sky-Tiger

Now it's time for us to add this portlet to the page. Go to C:\PlutoInstallation\pluto-1.0.1-rc1\webapps\pluto\WEB-INF\data. You will find two XML files there: pageregistry.xml and portletentityregistry.xml.
portletentityregistry.xml contains the definition of the portlet. Add these lines to it:  <application id="5">
   <definition-id>HelloWorld</definition-id>
     <portlet id="1">
       <definition-id>HelloWorld.HelloWorld</definition-id>
     </portlet>
    </application>
The <definition-id> of the application should be the name of the web application folder. The portlet's <definition-id> should be equal to the generated portlet-guid in web.xml.

pageregistry.xml defines which portlets to include on the page. Change it like this:   <fragment name="p2" type="portlet">
    <property name="portlet" value="5.1"/>
  </fragment>
Restart the Pluto server by first calling shutdown and then startup. Now go back to http://localhost:8080/pluto/portal and click on "Test Link"--it should show our HelloWorld portlet.
The right side of Figure 3 shows what your HelloWorld portlet will look like.

Sky-Tiger

How a Portal Page Is Created
Figure 4 shows how the separate portlets are assembled by the portal container to create the page.


Figure 4. Portal page creation

Most portal servers are basically web applications deployed in an application server, using a servlet for handling requests to the portal server. If you take a look inside of your Pluto installation, you will find out that Pluto is a normal web application, deployed in your Tomcat server. Take a look at C:\PlutoInstallation\pluto-1.0.1-rc1\webapps\pluto\WEB-INF\web.xml and you will find that org.apache.pluto.portalImpl.Servlet is mapped to get all requests pointed at the Pluto server.

Earlier, in "Elements of a Portal Page," we said that a portal page is made up of two types of content. One is content generated by various portlets on the page, and other is content generated by portal server.

In Pluto, whenever the user makes a request, control will go to the servlet. Depending on what page is requested by user, it will determine a list of portlets that need to be displayed. Once it has this list, it will pass control to these portlets in different threads and will collect content generated by them.

As for content contributed by the portal server (things like look and feel of the portal site and the decoration and controls for each portlet), the portal server depends on JSPs in the C:\PlutoInstallation\pluto-1.0.1-rc1\webapps\pluto\WEB-INF\aggregation folder. RootFragment.jsp is the main JSP, which decides the overall look and feel, and alignment. It includes Heads to decide what should be included in the <HEAD> tag of the generated page. Then it uses Banner.jsp to choose what should be displayed in the banner--by default, it will include pluto.png for displaying the banner. TabNavigation.jsp is used to decide the navigation scheme of the portal site. What this means is that you just need to change a few JSPs in this folder to change the whole look and feel of your portal site.

Depending on settings in pageregistry.xml, Pluto will decide how many rows a page should have, and use RowFragment.jsp to render it. It will use ColumnFragment.jsp to render each column. Then PortletFragmentHeader.jsp is used to render the header of every portlet; i.e., the title bar and the controls for minimize and maximize. footer.jsp is used to render the footer of the JSP. If you look at the HTML generated by portal page, you will find out that every portlet window is nothing but content inside a <TD> tag.

Sky-Tiger

Conclusion
For any new technology to be successful, it should have few qualities: first, it should leverage existing technology; second, it should solve common problems of existing technology; and third, it should provide you one more layer of abstraction. (As they say, every layer of abstraction solves half of the problems.)

The Portlet API has a very good chance of succeeding servlet technology, because it is capable of using the existing application server infrastructure. You can call an EJB from your portlet, or you can start and participate in a global transaction controlled by the application server. In other words, your portlet can do pretty much every thing that a servlet can do, in a much more business-logic-centric way.

Portlets provide you with a layer of abstraction because now you no longer have to worry about what HTTP method is used by the client, or create your own infrastructure to capture client events like button clicks. Last but not least, portlets solve most of the common problems of servlets by providing services for things like single-sign-on, personalization, etc.

freedom2k

一下发了这么多啊

freedom2k

这个还是值得看看的